Brain functional connectivity network breakdown and restoration in blindness

To characterize brain functional connectivity in subjects with prechiasmatic visual system damage and relate functional connectivity features to extent of vision loss.In this case-control study, resting-state, eyes-closed EEG activity was recorded in patients with partial optic nerve damage (n = 15) and uninjured controls (n = 13). We analyzed power density and functional connectivity (coherence, Granger causality), the latter as (1) between-areal coupling strength and (2) individually thresholded binary graphs. Functional connectivity was then modulated by noninvasive repetitive transorbital alternating current stimulation (rtACS; 10 days, 40 minutes daily; n = 7; sham, n = 8) to study how this would affect connectivity networks and perception.Patients exhibited lower spectral power (p = 0.005), decreased short- (p = 0.015) and long-range (p = 0.033) coherence, and less densely clustered coherence networks (p = 0.025) in the high-alpha frequency band (11-13 Hz). rtACS strengthened short- (p = 0.003) and long-range (p = 0.032) alpha coherence and this was correlated with improved detection abilities (r = 0.57, p = 0.035) and processing speed (r = 0.56, p = 0.049), respectively.Vision loss in the blind is caused not only by primary tissue damage but also by a breakdown of synchronization in brain networks. Because visual field improvements are associated with resynchronization of alpha band coherence, brain connectivity is a key component in partial blindness and in restoration of vision.